A regular logging truck is equipped with four scale pads, two of which are on the tractor and two of which are on the trailer. The tractor includes a log bunk pivotally supported therefrom and with a pair of scale pads disposed beneath opposite sides of the tractor log bunk. The trailer is also equipped with a log bunk and trailer scale pads are disposed under opposite sides of the trailer log bunk. The scale pads, when pressurized, elevate the log bunks and the load supported therefrom. The scale pads are pneumatically operated and are constructed to vent to the ambient atmosphere after being elevated a predetermined amount. As long as the tractor and trailer are disposed on reasonably level ground, the pressure required to maintain the scale pads elevated below their maximum elevation may be transposed into weight readings whereby the load supported from the bunks may be determined. However, in most instances, the areas in which the trucks are loaded with logs are not level resulting in uneven loading on the scale pads and if the scale pads are tilted and equipped with conventional side mounted pop-off valves, one pad will render a light reading, but in reality the true weight will be greater. The reason for this inaccurate weight reading is because the conventional side mounted pop-off valve is allowed to vent to the ambient atmosphere short of its lift. If a conventional scale pad is tilted downward on the side of the conventional side mounted pop-off valve, the weight reading will be light. The reason for this is that the scale pad is forced to travel further in order to vent to the ambient atmosphere. As a result, the scale pad is over-pressurized and thereby renders a heavy weight reading.
Accordingly, a need exists for scale pads which will be capable of rendering a true reading of the loading on corresponding log bunks, even if the truck being loaded is disposed on uneven ground.
Various forms of previously known scale pads and similar structures are disclosed in U.S. Pat. Nos. 2,020,307, 2,482,027, 2,646,272, 2,826,404, 2,867,432, 2,906,492 and 3,376,793.